Jasmonic acid improves barley photosynthetic efficiency through a possible regulatory module, MYC2-RcaA, under combined drought and salinity stress.

The combined stress of drought and salinity is prevalent in various regions of the world, affects several physiological and biochemical processes in crops, and causes their yield to decrease. Photosynthesis is one of the main processes that are disturbed by combined stress. Therefore, improving the photosynthetic efficiency of crops is one of the most promising strategies to overcome environmental stresses, making studying the molecular basis of regulation of photosynthesis a necessity. In this study, we sought a potential mechanism that regulated a major component of the combined stress response in the important crop barley (Hordeum vulgare L.), namely the Rubisco activase A (RcaA) gene. Promoter analysis of the RcaA gene led to identifying Jasmonic acid (JA)-responsive elements with a high occurrence. Specifically, a Myelocytomatosis oncogenes 2 (MYC2) transcription factor binding site was highlighted as a plausible functional promoter motif. We conducted a controlled greenhouse experiment with an abiotic stress-susceptible barley genotype and evaluated expression profiling of the RcaA and MYC2 genes, photosynthetic parameters, plant water status, and cell membrane damages under JA, combined drought and salinity stress (CS) and JA + CS treatments. Our results showed that applying JA enhances barley's photosynthetic efficiency and water relations and considerably compensates for the adverse effects of combined stress. Significant association was observed among gene expression profiles and evaluated physiochemical characteristics. The results showed a plausible regulatory route through the JA-dependent MYC2-RcaA module involved in photosynthesis regulation and combined stress tolerance. These findings provide valuable knowledge for further functional studies of the regulation of photosynthesis under abiotic stresses toward the development of multiple-stress-tolerant crops.

MicroRNA miR1118 contributes to wheat (Triticum aestivum L.) salinity tolerance by regulating the Plasma Membrane Intrinsic Proteins1;5 (PIP1;5) gene.

microRNAs (miRNAs) are important regulators of various adaptive stress responses in crops; however, many details about associations among miRNAs, their target genes and physiochemical responses of crops under salinity stress remain poorly understood. We designed this study in a systems biology context and used a collection of computational, experimental and statistical procedures to uncover some regulatory functions of miRNAs in the response of the important crop, wheat, to salinity stress. Accordingly, under salinity conditions, wheat roots' Expressed Sequence Tag (EST) libraries were computationally mined to identify the most reliable differentially expressed miRNA and its related target gene(s). Then, molecular and physiochemical evaluations were carried out in a separate salinity experiment using two contrasting wheat genotypes. Finally, the association between changes in measured characteristics and wheat salinity tolerance was determined. From the results, miR1118 was assigned as a reliable salinity-responsive miRNA in wheat roots. The expression profiles of miR1118 and its predicted target gene, Plasma Membrane Intrinsic Proteins1,5 (PIP1;5), significantly differed between wheat genotypes. Moreover, results revealed that expression profiles of miR1118 and PIP1;5 significantly correlate to Relative Water Content (RWC), root hydraulic conductance (Lp), photosynthetic activities, plasma membrane damages, osmolyte accumulation and ion homeostasis of wheat. Our results suggest a plausible regulatory node through miR1118 adjusting the wheat water status, maintaining ion homeostasis and mitigating membrane damages, mainly through the PIP1;5 gene, under salinity conditions. To our knowledge, this is the first report on the role of miR1118 and PIP1;5 in wheat salinity response.